The loads won't slid off the side, though. For years, I (with some friends) carted around canoes and kayaks using just two by fours between the boat and the car roof, and ropes tied front and back. One just has to make sure their ropes are tight enough, and the rope is tied in a V (narrow end at the boat, and wide end tied to the corners of the underside of the car front and back) so that it provides sideways stability. If one isn't hauling boats, they would need to tie the load together very carefully, and then tie the load to the front and back of the car using the V.